Many synthetic nitrofurans and related compounds are being used as chemotherapeutic agents or antibacterial food additives. Our previous studies with nitrofurans have shown that a chemotherapeutic agent, a food additive and an antischistosomal agent are mutagenic in Neurospora crassa. Our studies also show that a NO2 group at the C5 position and a particular side chain at the C2 position are necessary for the mutagenic activity of nitrofurans. It would be of interest to determine whether other chemotherapeutic agents are mutagenic in N. crassa, to verify function-structure relationship of nitrofurans and to determine the type of genetic alterations caused by chemotherapeutic agents. The ad-3-test system of N. crassa developed by de Serres is used in this study. With the system ad-3 mutants can be recovered and mutation frequencies can be determined. The isolated mutants can then be characterized by a series of genetic tests. Among 11 nitrofurans studied, nitrofurazon, AF-2, SQ18506, FANFT and H-193 are found to be mutagenic. Metronidazole, a well-known antitrichomonal drug used on women, is mutagenic only when the vegetative cultures of N. crassa are treated. Genetic characterization of ad-3 mutants induced by nitrofurans is still in process.